I just started to use VB.NET as my computer language to develop any Windows applications based on .NET framework. Before VB.NET, I use VB 6 to develop some special applications. I decided to use VB.NET Express Edition from Microsoft as my .NET IDE on my Windows. This is a good IDE, but I want to find any alternative open source .NET IDEs.
I found MonoDevelop and SharpDevelop. MonoDevelop is a cross platform .NET IDE that can be runned on Linux, MacOS, Windows, Salaris, and Unix. I have tried MonoDevelop on my fedora core 6 to create a simple application with VB.NET language. It will be a good alternative IDE. With Mono, your applications can be runned on those platforms which supported by Mono. You can think this like java virtual machine. Another alternative is SharpDevelop. This IDE can be runned only on Windows. So, this is my recommendation, if you want to focus for developing any applications only for Windows, Visual Studio 2005 Express Edition is better, but if you want to develop any cross platforms using .NET framework, you can use MonoDevelop.